328
METALLURGY OF IRON AND STEEL.
being given in Table XVI-P, and plotted in Curve BB, Fig. XVI-A.
The linear elongation of a fractured bar is made up of two factors. First, the excessive stretch in the immediate neighborhood of the break, due to the deformation known as "necking." Second, the "permanent set" throughout the rest of the bar. The first factor will bear a greater ratio to the sum total as the length grows less, and a less ratio as the length increases. Therefore, if the length of the piece is reduced so that it is all included in the region
60.-
45.-
40.-
35.-
aa-
26.-
20.-
AbKlsui
Ordin»te
\
—Length in Inchei —Perce itage of
Eloi'
10
13
U
18
18
20
Construction points.
No. Curve AA. Curve BB.
1 TT a=at a x= 8 x = 4 x = 5 x— 6 x— 7 at— 8 ..... 2 y — 47,43 4 y — 86.11 8 y*— 82.17 10 y — 28!96 12 y= 27.87 14 y — 26.78 x= 1.97 x= 8.94 X= 6.91 x= 7.87 x= 9.84 1=11.81 X— 18.78 x= 15.75 x= 17.72 y = 82io y = 29.8 y = 27.2 y=26.8 y=28.0 y=25.1 y=25.0 y = 24.»
• ....
FIG. XYI-A.—ELONGATION WITH VARYING LENGTH.
of necking, as, for instance, when the piece is only 2 inches long, the percentage of elongation will increase rapidly. On the other hand, when the length is increased beyond 14 inches, the ratio of